rcu: Move rcu_barrier_mutex to rcu_state structure

In order to allow each RCU flavor to concurrently execute its
rcu_barrier() function, it is necessary to move the relevant
state to the rcu_state structure.  This commit therefore moves the
rcu_barrier_mutex global variable to a new ->barrier_mutex field
in the rcu_state structure.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcutree.c

@@ -71,6 +71,7 @@ static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
 	.onofflock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.onofflock), \
 	.orphan_nxttail = &sname##_state.orphan_nxtlist, \
 	.orphan_donetail = &sname##_state.orphan_donelist, \
+	.barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
 	.fqslock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.fqslock), \
 	.n_force_qs = 0, \
 	.n_force_qs_ngp = 0, \
@@ -155,10 +156,6 @@ static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
 unsigned long rcutorture_testseq;
 unsigned long rcutorture_vernum;
 
-/* State information for rcu_barrier() and friends. */
-
-static DEFINE_MUTEX(rcu_barrier_mutex);
-
 /*
  * Return true if an RCU grace period is in progress.  The ACCESS_ONCE()s
  * permit this function to be invoked without holding the root rcu_node
@@ -2303,7 +2300,7 @@ static void _rcu_barrier(struct rcu_state *rsp)
 	init_rcu_head_on_stack(&rd.barrier_head);
 
 	/* Take mutex to serialize concurrent rcu_barrier() requests. */
-	mutex_lock(&rcu_barrier_mutex);
+	mutex_lock(&rsp->barrier_mutex);
 
 	smp_mb();  /* Prevent any prior operations from leaking in. */
 
@@ -2380,7 +2377,7 @@ static void _rcu_barrier(struct rcu_state *rsp)
 	wait_for_completion(&rsp->barrier_completion);
 
 	/* Other rcu_barrier() invocations can now safely proceed. */
-	mutex_unlock(&rcu_barrier_mutex);
+	mutex_unlock(&rsp->barrier_mutex);
 
 	destroy_rcu_head_on_stack(&rd.barrier_head);
 }

kernel/rcutree.h

@@ -400,6 +400,7 @@ struct rcu_state {
 	struct task_struct *rcu_barrier_in_progress;
 						/* Task doing rcu_barrier(), */
 						/*  or NULL if no barrier. */
+	struct mutex barrier_mutex;		/* Guards barrier fields. */
 	atomic_t barrier_cpu_count;		/* # CPUs waiting on. */
 	struct completion barrier_completion;	/* Wake at barrier end. */
 	raw_spinlock_t fqslock;			/* Only one task forcing */